The proposed studies are concerned primarily with enzymes particular to myelination, transport across the myelin sheath and the maintenance of myelin. Part of the project will include a continuation of the studies of the carbonic anhydrase, 5'-nucleotidase and 2',3'-cyclic nucleotide-3'-phosphohydrolase in myelin and cells. As CNS cell isolation methods become modified, the activities of these enzymes in neurons and astrocytes will be reassessed and the activities in oligodendrocytes from gray matter and white matter will be compared. In the PNS these enzymes will be assayed in Schwann cell and myelin fractions after nerve transection. 5'-Nucleotidase will be isolated from myelin and used for immunocytochemical localization in the developing rat CNS and PNS; similar studies will utilize carbonic anhydrase isolated from rat erythrocytes. Pilot studies to identify new myelin-associated enzymes will involve assays of several transport enzymes in purified myelin, and, similarly, some enzymes, including several of the pentose phosphate pathway, will be assayed in developing oligodendrocytes. Oligodendrocyte-enriched enzymes, including glycerolphosphate dehydrogenase, will be measured in myelin-related fractions, as an approach to the anatomical relationships of those membranes to the myelinating cells. Enzyme studies using brain homogenates and myelin in hypomyelinating mutant mice will be an additional approach to metabolism related to myelination. The results of these studies should make it possible to infer some of the special adaptations of oligodendrocytes and Schwann cells to meet the requirements for energy, raw materials and cofactors during myelination and myelin maintenance. With further interpretation it should become possible to postulate what sorts of stress could damage myelin and how those stresses could be prevented.